Cracking

Question 1

Thermal Cracking

Answer 1

; propagation of damage in early age

; affected by fly ash content and cement fineess

Question 2

Shrinkage Cracking

Answer 2

; propagation of damage in early age

Question 3

example of change in load demand

Answer 3

; seismic load adaptation ( although it is not deteriorating concrete )

; traffic increase

; extreme weather conditions

Question 4

Thermal stress

Answer 4

; due to steep temp. gradients

Question 5

strain and stress

Answer 5

; change of strain = coeff * change of Temp.

; change of stress = E * change of strain

Question 6

Two types of thermal variations casing cracking

Answer 6

; space : heat differences btw one generated by hydration(exothermic) and the other surrounding environment

; time : example would be stripping off insulation too early when concrete is still warm

Question 7

Prevention of thermal cracking

Answer 7

; Insulation molds ( same material on both sides)

; leave insulation longer

; consider retardant

; Fly ash b/c slow setting time

; Temp. curing

; fiber reinforcement

; more agg.

Question 8

Fiber reinforcement

Answer 8

; restrain deformation

; hold crack edges

Question 9

Autogenous shrinkage

Answer 9

; when water is removed surface tension generate deformation

; caused by lower w/c ratio

; withdrawal of capillary pore water for the hydration = this process aka self desiccation

Question 10

self desiccation

Answer 10

; leads to volume contraction

; early age cracking